swift - 如何测试命名元组的 Swift 数组的相等性

Question

Swift 元组不是 Equatable，作为复合类型，它们不能通过协议(protocol)扩展变成 Equatable。解决方法 ( as documented in another answer ) 是为每个元组元数的 == 运算符创建一个重载。

有趣的是，可以为常规元组声明 == 运算符，并使用它来比较元组与命名字段:

func ==<T1: Equatable, T2: Equatable>(lhs: (T1,T2), rhs: (T1,T2)) -> Bool {
    return lhs.0 == rhs.0 && lhs.1 == rhs.1
}

var one = ("One", 1)
let two = ("Two", 2)
print(one == two) // "false"

typealias NamedTuple2 = (name: String, value: Int)
var namedone: NamedTuple2 = (name: "One", value: 1)
let namedtwo: NamedTuple2 = (name: "Two", value: 2)
print(namedone == namedtwo) // "false"
print(namedone == one) // "true"

元组数组也需要自定义重载才能作为一个整体进行比较:

func ==<T0: Equatable, T1: Equatable>(lhs: [(T0, T1)], rhs: [(T0, T1)]) -> Bool {
    if lhs.count != rhs.count {
        return false
    }
    for (index, value) in lhs.enumerate() {
        if !(value == rhs[index]) {
            return false
        }
    }
    return true
}

let array12: [(String, Int)] = [one, two]
let array3: [Tuple2] = [("Three", 3)]
print(array12 == array3) // "false"

但是，此运算符不接受命名元组数组:

let namedarray12: [NamedTuple2] = [namedone, namedtwo]
let namedarray3: [NamedTuple2] = [array3[0]]
print(namedarray12 == namedarray3)
// error: binary operator '==' cannot be applied to two '[NamedTuple2]' operands

有没有一种方法可以测试命名元组数组的相等性，而无需为特定命名元组声明 == 的重载？

Answer 1

SequenceType.elementsEqual(_,isEquivalent:) 方法接受用于比较元素的谓词。相同的 == 重载适用于命名和未命名的元组。因此，与其尝试将 == 应用于整个数组，不如使用 elementsEqual。

func ==<T1: Equatable, T2: Equatable>(lhs: (T1,T2), rhs: (T1,T2)) -> Bool {
    return lhs.0 == rhs.0 && lhs.1 == rhs.1
}

let namedarray: [(name: String, value: Int)] = [(name: "One", value: 1), (name: "Two", value: 2)]
// namedarray == namedarray12
namedarray.elementsEqual(namedarray12, isEquivalent: ==) // true